Red Leaf Spot

Exobasidium rostrupii (Nannfeldt)

Symptoms: Red leaf spot is characterized by the presence of circular, bright red spots on the upper sides of leaves and occasionally on young green berries. The undersides of the leaf spots are paler and eventually become covered with a dense, white, powdery deposit. When several spots develop on a single leaf, they often grow together. Infected leaves are usually shed prematurely. Leaf infections may spread through the petiole (leaf stem) to the young growing vine, causing reddening and death of the stem. The part of the vine above the infected area may continue its normal growth or wither and die, depending on the amount of distortion of the stem tissue. Excessive nitrogen use will favor the onset of this disease. [Ben Lear variety is especially prone to this disease. Stevens variety is more immune to it than any other variety in Maine.]

Control: The early stage of this disease is no cause for panic, and generally sprays for fruit rot control will also control this disease. Copper compounds will offer protection against further infection. Injured plants will not be cured by the copper, but it can slow or stop the spread of the infection.